40 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



dered from the firm of Alvan Clark & Sons, Cambridgeport, 

 Massachusetts, and it is probable that nearly all the appara- 

 tus will be' of American manufacture. 



The commission has printed a pamphlet containing some 

 important papers on the subject, and it is expected that this 

 will be followed by others. The present pamphlet is mostly 

 devoted to the question of photographing the transit. It 

 contains a very full description of the apparatus used by Mr. 

 L. M. Rutherford, of New York, whose photographs of the ce- 

 lestial bodies are the finest ever taken. The longest paper 

 is by Professor Newcomb, one of the commission, who gives 

 a detailed description of the method by which the commis- 

 sion actually proposes to take the photographs. Professor 

 NTewcomb finds objections which he deems fatal to nearly all 

 the plans of photographing that have been proposed in Eu- 

 rope, and therefore proposes that adopted by Professor Win- 

 lock, of the observatory of Harvard College. In this plan the 

 telescope is forty feet long, and is fixed in a horizontal posi- 

 tion, the object end pointing north. A short distance from 

 the object-glass is a plain mirror, which is set so as to throw 

 the rays of the sun into the telescope. At the other end of 

 the telescope an image of the sun four and a half inches in 

 diameter is formed, and here the photographic plate is placed 

 to receive and photograph this image. Immediately in front 

 of the plate a plumb-line is to be hung, and thus be photo- 

 graphed on the plate, in order to get the direction of the ver- 

 tical diameter of the sun. 



Among the advantages claimed for this plan are : That the 

 photograph can be taken in the dark room, and on a firm sup- 

 port (while, by the other plan, the photographer must take 

 his sensitive plate to the eye-piece of the telescope, which has 

 to be kept in motion) ; that the image on the plate is free 

 from distortion ; and, finally and chiefly, that it is the only 

 plan by which the measures of inches, on the negative, can be 

 reduced to minutes and seconds of an arc in the heavens with 

 the necessary accuracy. 



